The present invention relates to a rubber extruding method and a rubber extruding apparatus, capable of performing extruding of a rubber extruded intermediate having a thickness varying in the width direction with good precision.
In a case where a raw tire (green tire) is produced, for example, rubber extruded intermediates such as a sidewall rubber, a clinch rubber, a tread rubber and others are employed. Such rubber extruded intermediates are extruded from a rubber extruder having a die plate. In FIG. 10(A), a tread rubber xe2x80x9caxe2x80x9d is illustrated as such a rubber extruded intermediate. In general, these rubber extruded intermediates xe2x80x9caxe2x80x9d are each extruded as an article having a thickness varying in a width direction.
In extrusion, rubber flows with more of ease in a portion a1 having a larger thickness in the rubber extruded intermediate xe2x80x9caxe2x80x9d, as compared with a portion a2 having a smaller thickness therein. For this reason, a distribution vp of an extruding speed v, as shown in FIG. 10A, is profiled with a value different according to a portion like a sectional shape of the rubber extruded intermediate. That is, the extruding speed v is non-uniform in the width direction. Furthermore, if an extruding rate of an extruder varies, the extruding speed distribution vp loses more of balance thereof, easily accelerating non-uniformity in extruding speed to an greater extent. In such a case, there arises a problem that passage resistance of rubber passing through the die plate largely varies at positions along the width direction, thereby causing a sectional shape of a rubber extruded intermediate not to be constant.
The present invention has been contrived in light of the problems as described above and it is an object of the present invention to provide a rubber extruding method and a rubber extruding apparatus, working to maintain a sectional shape of a rubber extruded intermediate to be constant even in a case where an extruding rate of an extruder or the like varied.
According to the first present invention is a rubber extruding method extruding a rubber extruded intermediate by discharging rubber from a discharge port of a die plate mounted to an outlet of an extruder, wherein
said die plate has an inflow port through which rubber flows in from the extruder side,
said discharge port, and
a rubber flow path connecting said inflow port and said discharge port therebetween,
said discharge port is of a flat shape with a lower section having a smaller height and a higher section having a larger height and with a height varying along a width direction to thereby extrude said rubber extruded intermediate with a thickness varying along a width direction, and
in addition each extruding speed of said rubber extruded intermediate is made uniform at positions along a width direction thereof.
According to the second present invention is a rubber extruding apparatus extruding a rubber extruded intermediate by discharging rubber from a discharge port of a die plate mounted to an outlet of an extruder, wherein
said die plate has an inflow port through which rubber flows in from the extruder side,
said discharge port, and
a rubber flow path connecting said inflow port and said discharge port therebetween,
said discharge port is of a flat shape with a lower section having a smaller height and a higher section having a larger height and with a height varying along a width direction to thereby extrude said rubber extruded intermediate with a thickness varying along a width direction, and
said die plate satisfies the following relation:
(Ssi/Sso) greater than (Shi/Sho),
xe2x80x83wherein Sso is an area per unit width in said lower section, Ssi is an area at said inflow port through which rubber flowing through said area Sso per unit width in said lower section passes, Sho is an area per unit width in said higher section and Shi is an area at said inflow port through which rubber flowing through said area Sho per unit width in said higher section passes.